Arsenate cement or cement mixture



106. COMPOSlTlONS,

COATING R PLASTIC.

Patented Jan. 21, 1936 UNITED STATES PATENT OFFICE ARSENATE CEMENT OR CEMENT MIXTURE Sweden No Drawing. Application February 25, 1935, Serial No. 8,079. In Sweden January 13, 1934 4 Claims.

The present invention relates to hydraulically binding cements or cement mixtures containing calcium arsenate (compound of quinquevalent arsenic oge er with lime, calcium silicate f. l.

5 in the form of blast momma cement, aluminate cenmm EEO clue s or ec ica purposes. The calcium arsenate used for the purpose in question may suitably have a composition corresponding to meta-arsenate (Cao-Aszos) and/or pyroarsenate (2CaO-AS2O5), or an intermediate or neighbouring composition, i. e. acid arsenates with deficiency of lime in relation to the tri-basic arsenic acid. Upon the hydrating the acid arsenate l5 fixes lime and is converted into diflicultly soluble orthoarsenate (BCaO-AsZOs-aq). The setting time can be regulated with the degree of acidity of the arsenate. Good properties may be obtained with cements or cement mixtures contain- 20 ing 20 to 80 percentage by weight of calcium arsenate.

It has been previously proposed to use arsenious acid (compound of trivalent arsenic) for the production of a difiicultly soluble and cheap ee- 25 ment and such cement types have also been worked out, in the production of which it has proved in some respects to be particularly suitable to use, on the one hand, a mixture of '70 parts by weight of Portland cement together with 30 30 parts by weight of arsenious acid (AS203) and, on the other hand, a mixture of 75 to 80 parts by weight of dicalcium silicate (chiefly of gamma type) together with 25 to 20 parts of arsenious acid. There has also been ascertained a con- 36 siderable reduction of the solubility of such a mixture as compared with ordinary Portland cement, which reduction may be owing to the formation of difiicultly soluble calcium arsenites (for instance ZCaOASZOS'EQ). As regards the 40 Portland cement mixture, the formation of the calcium arsenite implies a simultaneous fixation of the excess of lime arising upon the hydrating oi the Portland cement. However, these arsenious acid cements have also certain undesirable properties. The strength is less than I. i. that of Portland cement of class A; the cement as set is not quite resistant to carbonic acid (carbon dioxide), and, finally, the general fear of the poisonous efiect of the arsenic, especially that of the arsenious acid, is a serious hindrance to their use in practice.

However, the arsenic cements are not afiected with these disadvantageous properties. The strength and the low solubility are increased, 1 since the calcium arsenates are more stable, better crystallizing and more diflicultly soluble than the corresponding arsenite. The stability with relation to carbonic acid is greater than for arsenite. Last but not least, the fear of the poisonous efiect may be met with the information as to the fact that, in the arsenate cements, the arsenic has been converted into compounds which, in fact, are not more dangerous than f. i. the red lead in common use in building engineering.

Having thus described my invention I declare that what I claim is:-

1. A cement mixture containing a calcium arsenate with a composition corresponding to one of the following: meta-arsenate (Cao-Aszos) or pyroarsenate (2CaO'AszO5), together with one of the following: lime, calcium silicate, Portland cement, aluminate cement.

2. Cements or cement mixtures as claimed in claim 1, characterized in that they contain 20 to 80 percentage by weight of calcium arsenate.

3. A cementitious mixture, comprising a calcium arsenate from among the calcium arsenate compounds intermediate the meta and the pyro, together with one of the following: lime, calcium silicate, Portland cement, aluminate cement.

4. A cementitious mixture, comprising a calcium arsenate from among the calcium arsenate compounds adjacent the meta and the pyro compounds, together with one of the following: lime, calcium silicate, Portland cement, aluminate cement.

JOHAN BERTIL STALHANE. 

